The present invention relates to an arrangement for determining the relative angular orientation between a first machine element and a second machine element and, more particularly, to an arrangement for determining the relative angular orientation of an excavator bucket with respect to the dipper stick of the excavator.
Control systems have been developed for monitoring and automatically controlling the operation of various types of construction equipment, such as for example excavators. Such systems of this general type are disclosed in U.S. Pat. No. 5,461,803, issued Oct. 31, 1995, to Rocke; U.S. Pat. No. 5,062,264, issued Nov. 5, 1991, to Frenette et al; and U.S. Pat. No. 4,964,779, issued Oct. 23, 1990, to Sagaser. In each of these patents, a positioning and control system is disclosed that includes an arrangement for measuring the relative positions of various machine elements, comparing the measured positions with the desired positions in a feedback control system, and adjusting the machine element positions accordingly. In the Rocke patent, displacement sensors sense the amount of piston rod extension in the boom, dipper stick, and bucket hydraulic actuators. To accomplish this, a radio frequency sensor is provided inside each of the hydraulic cylinders. The sensor includes a pair of loop antennas that transmit and receive radio frequency electromagnetic signals, exciting a transverse electromagnetic field in the cavity when the frequency of the signal corresponds to the resonant frequency of the cavity. The resonant frequency of the cavity is primarily dependent upon the longitudinal length of the cavity. Therefore, a voltage controlled oscillator acts under the control of a sawtooth voltage waveform a function generator to deliver a variable frequency signal to the first loop antenna. An RF detector monitors the second loop antenna for an indication that the resonant frequency has been reached. At resonance, a microprocessor samples the output of the voltage-controlled oscillator and correlates the resonant frequency to the length of the coaxial cavity.
The Frenette patent suggests that angle encoders at the pivot points between machine elements may be used to measure the relative positions of these machine elements. Alternatively, the Frenette patent suggests that a sensor measuring the displacement of an actuator, or a camera recording the location of the machine elements may be used. Finally, the Sagaser patent discloses the use of a special hydraulic actuator that includes a specially constructed potentiometer arrangement inside the actuator that varies in electrical resistance in relation to the extension of the piston rod.
These arrangements are expensive, require special parts, and may require frequent service adjustments. Further, the length of time required for servicing such arrangements may be longer than is desirable, due to the need to disassemble the actuators or other components. Accordingly, it is seen that there is a need for a simple, rugged, reliable, and economical arrangement for determining the relative angular orientation between a first machine element and a second machine element.
These needs are met by an arrangement according to the present invention for determining the relative angular orientation between a first machine element and a second machine element. For example, the present invention may be used to determine the angular orientation of an excavator bucket with respect to the dipper stick of an excavator. The excavator bucket is mounted on a bucket linkage that is pivotally secured to the end of the dipper stick. The machine further includes a linear actuator having a first actuator element pivotally connected to the first machine element and a second actuator element pivotally connected to the second machine element. The first and second actuator elements are linearly moveable with respect to each other, whereby relative linear movement of the actuator elements causes relative pivotal movement between the first and second machine elements. The linear actuator preferably an hydraulic actuator, with the first actuator element comprising an hydraulic cylinder pivotally connected to the dipper stick, and the second actuator element comprising a piston rod pivotally connected to the bucket linkage. Extension or contraction of the hydraulic actuator causes the excavator bucket to be pivoted by the bucket linkage with respect to the dipper stick. This arrangement includes a cable extension linear position transducer having a transducer casing, a sheath extending from the casing, and an extensible cable extending from the sheath. The transducer provides an electrical output related to the extension of the cable from the sheath. A transducer mounting secures the casing of the cable extension linear position transducer in fixed relationship to the hydraulic cylinder. A clip secures the extensible cable to the piston rod. By this arrangement, extension or contraction of the hydraulic actuator causes the output of the transducer to vary, thus providing an electrical output indicating the relative angular orientation of the excavator bucket with respect to the dipper stick.
The clip includes a band around the piston rod, strapping the cable to the piston rod adjacent to the bucket linkage. A mounting is provided for securing the sheath to the hydraulic cylinder near the end of the cylinder from which the piston rod emerges. The sheath includes a rigid end portion from which the cable extends. The rigid end portion includes an outer rigid tube, an inner rigid tube within the outer rigid tube, and a flexible liner within the inner rigid tube. The rigid end portion is oriented such that the cable emerges from the rigid end portion in close proximity to the piston rod and extends in close proximity to the piston rod. The cable extension linear position transducer is mounted such that the sheath and extensible cable extend along the cylinder and the piston rod on the sides thereof generally facing the dipper stick. By this arrangement, the sheath and extensible cable are partially protected by the cylinder and piston rod. The cable extension linear position transducer may be mounted such that the sheath and extensible cable both extend along the cylinder and the piston rod on the side thereof generally, but not directly facing the dipper stick. Alternatively, the sheath and extensible cable may extend along the cylinder and the piston rod on the side thereof directly facing the dipper stick. By these arrangements, the sheath and extensible cable are protected by the cylinder and piston rod. The extensible cable includes a first cable portion extending from the transducer casing, and a second cable portion extending from the sheath. The first and second cable portions are attached together within the sheath.
In an alternative arrangement, the second cable portion extending from the sheath comprises a flexible belt. This flexible belt attaches to the first cable portion within the sheath. Additionally, in this embodiment the mounting provided for securing the sheath to the hydraulic cylinder near the end of the cylinder from which the piston rod emerges also supports a pulley system for guiding and positioning the flexible cable parallel to the piston rod. Further, the sheath is a flexible tube that is sized to allow the belt to move without obstruction therewithin.
In another alternative arrangement, an end of the extensible cable that extends from the sheath is releasably secured by a release mechanism. This release mechanism is secured to the piston rod by the band. Should the extensible cable get snag on an obstruction, the release mechanism will release the secured end of the extensible cable if a certain amount of pull resistance in the reverse direction is overcome by a force. Should it also become necessary to remove the end of the extensible cable from the release mechanism, the release mechanism will release the secured end if a certain amount of pull resistance in the forward direction is overcome by a force. Additionally, the release mechanism prevents the hard bending of the extensible cable at its end by allowing the releasably secured end to rotate through the range of movement of the dipper stick.
Accordingly, it is an object of the present invention to provide an improved arrangement for monitoring the relative angular orientation between a pair of pivotally linked machine parts; to provide a sturdy, simplified mechanism for such monitoring; and to provide an accurate arrangement for accomplishing such monitoring.
It is a further object of the invention to provide an improved arrangement for monitoring the relative angular orientation between a pair of pivotally linked machine parts with a simplified mechanism that functions properly in all encountered work conditions.
Other objects and advantages of the invention will be apparent from the following detailed description, the accompanying drawings, and the appended claims.